Let the subgroup $G$ of elliptic curve constructed with point $P$ with prime order $q$ by $G=\langle P\rangle $. The $h(x)$ is a hash function. We want to map the hash of arbitrary message $m$ to a point in $G$ for use in the signature algorithm (such as BLS).
Why we don't use $k=h(m) \bmod q$ and then $S=kP$, whereas it is clear that the point $S$ is in $G$? What is the flaw of this? security or efficiency?